This invention relates to a photographic support consisting essentially of a substrate and a resin layer provided at least on the side of the substrate where images are to be formed (hereinafter referred to as "image-forming side"), said resin layer comprising a specific titanium dioxide pigment, etc. More particularly, this invention relates to a photographic support which has a high lightness and a high apparent whiteness, the apparent whiteness being highly stable, and has good surface property on which a highly sharp printed image can be formed and is quite a little in generation of die lip stain at production.
A so-called resin-coated paper for photograph which comprises a substrate at least one side of which is coated with a resin composition comprising titanium dioxide pigment and a polyolefin resin has been known as photographic support. For example, U.S. Pat. No. 3,501,298 discloses a photographic support comprising a paper substrate, both sides of which are coated with a polyolefin resin. Since rapid development treatment has been employed, a polyethylene resin coated paper for photograph comprising a base paper for photographic paper, both sides of which are coated with a polyethylene resin has mainly been practically used as a support for photographic support, titanium dioxide pigment being usually contained in the resin on the image-forming side to give sharpness to images formed thereon.
Hitherto, anatase type and rutile type titanium dioxide pigments have been known as those which are to be contained in the resin layer on the image-forming side of resin-coated paper for photograph. The following titanium dioxide pigments are also known: A titanium dioxide pigment, the surface of which is not subjected to coating treatment; a titanium dioxide pigment, the particles of which are subjected to coating treatment with an inorganic material such as hydrated aluminum oxide, hydrated silicon oxide or the like as disclosed in Japanese Patent Application Kokai Nos. 52-35625 and 57-108849; and a titanium dioxide pigment, the particles of which are subjected to coating treatment with an organic material such as a polyhydric alcohol or a derivative thereof, a polyorganosiloxane or a derivative thereof, or the like as disclosed in Japanese Patent Application Kokai No. 52-35625, Japanese Patent Application Kokoku Nos. 58-43734 and 61-26552 and the like.
Furthermore, several resin-coated papers have been known as photographic supports when especially high sharpness of printed image is required. Examples thereof are as follows: (1) a resin-coated paper which contains a titanium dioxide pigment in the resin layer in a high concentration; (2) a resin-coated paper which contains a rutile type titanium dioxide pigment in the resin layer; (3) a resin-coated paper which contains titanium dioxide in the resin layer with addition of surfactants represented by a metal soap such as zinc stearate, calcium stearate, zinc palmitate and the like; and (4) a resin-coated paper which contains, in the resin layer, a so-called organic material-treated titanium dioxide pigment, the particles of which has been subjected to coating treatment with the organic material as mentioned above.
However, the above photographic supports suffer from some severe problems in sharpness of image and other photographic properties and processability and thus are still not satisfactory.
First, when concentration of titanium dioxide pigment in the resin layer of polyolefin resin-coated paper is increased as in the above (1), a photographic support which can provide printed image of high sharpness can be obtained, but severe problems often occur in photographic properties and productivity. That is, when a polyolefin resin composition, especially a polyethylene resin composition containing titanium dioxide pigment is melt-extruded into a film from a slit die and coated on a substrate, deposits or stains in the form of needles or iciles (hereinafter referred to as "die lip stain") tend to be formed on the tip of die lip in a short time. The die lip stain is very troublesome because it tends to grow larger with the lapse of time. If this die lip stain is formed at the melt-extrusion coating, streaks are formed in machine direction on the surface of the polyolefin resin-coated paper or streak-like flaws are generated due to nonuniform amount of coated resin. Furthermore, the die lip stain sometimes sticks to the substrate to form a foreign matter. Thus, the surface property of the polyolefin resin-coated paper is considerably damaged and such polyolefin resin-coated paper is unsuitable as photographic support which requires superior surface property and loses commercial value. Moreover, in order to completely remove the die lip stain once formed, production must be stopped to clean die lip or exchange die lip. Therefore, much labor and time are required and thus causes considerable reduction of productivity.
Since titanium dioxide pigment contained in the resin layer of polyolefin resin-coated paper for photograph is subjected to severe requirements in its quality, mainly used is a so called inorganic compound-treated titanium dioxide pigment, the particles of which are subjected to a coating treatment with inorganic compounds such as hydrated aluminum oxide and hydrated silicon oxide and a so-called untreated titanium dioxide pigment which is subjected to no surface treatment is scarcely used. However, when inorganic compound-treated titanium dioxide pigment is used, the larger the number of treatments of the titanium dioxide pigment with inorganic compound, the more the die lip stain formed. On the other hand, when untreated titanium dioxide pigment is used, the resin layer undergoes conspicuous deterioration by light and besides much discoloration with time, although die lip stain occurs less.
In order to solve these problems, for example, Japanese Patent Application Kokai No. 57-108849 discloses a photographic support containing a titanium dioxide pigment, the surface of which is lightly treated with hydrated aluminum oxide. However, this photographic support also has the problems that some die lip stains occur when content of the titanium dioxide pigment in the polyolefin resin composition is considerably increased to obtain printed images of high sharpness.
When a rutile type titanium dioxide pigment is used as titanium dioxide pigment contained in resin layer of polyolefin resin-coated paper as in the above (2), a photographic support which can provide printed images of fairly high sharpness can be obtained as compared with when anatase type titanium dioxide pigment is used. However, another serious problems on photographic properties occur. That is, the resin layer containing titanium dioxide pigment on the image-forming side of the photographic support tends to yellow due to the rutile type titanium dioxide and a printed image having vivid white ground cannot be obtained.
The inventors have found that even if surfactants represented by metallic soaps such as zinc stearate, calcium stearate and zinc palmitate are added when titanium dioxide pigment is contained in resin layer of polyolefin resin-coated paper as in the above (3), sharpness of printed image on the resulting photographic polyolefin resin-coated paper cannot substantially be improved.
Incorporation of titanium dioxide pigment into resin layer of polyolefin resin-coated paper is generally carried out in the following manner: That is, so-called masterbatch comprising the resin and the pigment contained in a high concentration in the resin is prepared by usual melt-kneading machines such as Banbury mixer, kneader and extruder for kneading and this masterbatch is diluted to desired concentration to obtain a polyolefin resin composition, which is coated on a substrate by melt-extrusion. Alternatively, a so-called compound comprising the resin and the pigment contained originally at a desired ratio in the resin is prepared and this compound is coated on a substrate by melt-extrusion.
The main object of containing metallic soap in polyolefin resin-coated paper for photograph is to improve peelability of resin-coated paper from cooling roll of melt extruder in coating resin on a substrate by melt-extrusion.
However, as a result of the research conducted by the inventors, an utterly new fact has been found on the effect of metallic soap contained in resin-coated paper. That is, it has been found that when the metallic soap added in preparation of masterbatch or compound of titanium dioxide pigment is contained in the resin layer in an amount of less than 1.5% by weight based on the weight of titanium dioxide pigment and in an amount of less than 0.15% by weight based on the weight of resin layer, sharpness of printed image increases with increase in the content, but the peelability referred to above is inferior with such content and furthermore, when the metallic soap is contained in an amount of 1.5-7.5% by weight based on the weight of titanium dioxide pigment and in an amount of 0.15-0.75% by weight based on the weight of resin layer, the peelability is improved with increase in the content, but sharpness of printed image is considerably lowered and sometimes becomes lower than when no metallic soap is contained. Furthermore, when metallic soap is contained in an amount of more than 7.5% by weight based on the weight of titanium dioxide pigment and in an amount of more than 0.75% by weight based on the weight of resin layer, sharpness of printed image gradually decreases with increase in the addition amount of the metallic soap and generation of oily smoke increases and processability at melt-extrusion coating of resin composition becomes much inferior. As explained above, even if a metallic soap is added at the time of incorporation of titanium dioxide pigment in resin layer of polyolefin resin-coated paper, there is the problem that photographic support which can afford high sharpness of printed image cannot be obtained.
Furthermore, the inventors have found that even when a so-called organic compound-treated titanium dioxide pigment is used as the titanium dioxide pigment to be contained in resin layer of polyolefin resin-coated paper for photograph as in the above (4), sharpness of printed image is not improved. Moreover, when a metallic soap represented by zinc stearate in such an amount as can give sufficient peelability at preparation of resin-coated paper is added together with an organic compound-treated titanium dioxide pigment to resin layer of polyolefin resin-coated paper, sharpness of printed image on the resin-coated paper is nearly the same as or only slightly higher than when titanium dioxide pigment which has not been treated with organic compound is used.
On the other hand, there have been known some techniques to improve whiteness of resin layer containing titanium dioxide pigment on the image-forming side of resin-coated type photographic supports.
U.S. Pat. No. 3,501,298 discloses that a blue inorganic pigment such as ultramarine, cobalt blue or the like, a red inorganic pigment such as oxidized cobalt phosphate (e.g., Raspberry V-6260 manufactured by Ferro Colors Corp.), or a red organic pigment such as quinacridone red is contained in the resin layer in addition to the titanium dioxide pigment. It is also known to contain a fluorescent agent having bis(alkyl-substituted benzoxazolyl)thiophene structure which is represented by Uvitex OB (trademark for the product manufactured by Ciba Geigy) in resin layer. Japanese Patent Application Kokai No. 51-6531 discloses to contain a titanium dioxide pigment treated with hydrated alumina and a fluorescent agent in resin layer. Japanese Patent Application Kokai No. 53-19021 discloses to contain a blue inorganic pigment such as ultramarine and a red inorganic pigment such as Daiichi Pink DP-1 or Daiichi Violet DV-1 (manufactured by Daiichi Kasei Co.). Further, Japanese Patent Application Kokoku 56-51336 discloses to contain a fluorescent agent having bis(alkyl substituted benzoxazolyl)naphthalene structure in the resin layer. Japanese Patent Application Kokai No. 61-75341 discloses a technique to incorporate a quinacridone red organic pigment in resin layer. Moreover, U.S. Pat. No. 4,794,071 discloses to contain a mixture of bis(benzoxazolyl)stilbene fluorescent agents.
However, the above enumerated techniques have the following defects.
First, in the technique for improving apparent whiteness of resin layer by diminishing the tendency of yellowing of the resin layer caused by titanium dioxide pigment contained therein at a high concentration by containing an inorganic or organic coloring pigment or coloring dye in a resin layer on the image-forming side of resin-coated paper type photographic support, since color of resin layer is apparently whitened by coloration, brightness is lowered and vivid whiteness cannot be obtained.
Secondly, it has also been found that when a polyolefin resin composition containing a fluroescent agent, especially a bis(benzoxazolyl)naphthalene type fluorescent agent or a bis(benzoxazolyl)stilbene type fluorescent agent and a titanium dioxide pigment, especially an inorganic compound-treated titanium dioxide pigment is melt-extruded into a film from a slit die and coated on a substrate, die lip stain occurs much and, especially when the resin composition additionally contains inorganic or organic color pigment or color dye, especially blue pigment or blue dye, die lip stain is especially conspicuous. Furthermore, as a result of investigation conducted by the inventors, it has been found that considerable die lip stain occurs when a polyolefin resin composition containing an inorganic or organic color pigment or color dye (especially, inorganic color pigment) and a titanium dioxide pigment (especially inorganic compound-treated titanium dioxide pigment) is melt-extruded into a film from a slit die and coated on a substrate.
Thirdly, when whiteness of resin layer is improved by containing in the resin layer a fluorescent agent of bis(benzoxazolyl)thiophene structure having a substituent as mentioned in U.S. Pat. No. 3,449,257 or a fluorescent agent of bis(benzoxazolyl)naphthalene structure having a lower alkyl group of 5 or less carbon atoms as mentioned in Japanese Patent Application Kokoku No. 56-51336, the fluorescent agent tends to bleed out of the resin layer and stability of color tone is inferior and besides, adhesion between resin layer and photographic emulsion layer is insufficient. In addition, a photographic support containing the above fluorescent agent is inferior in stability of whiteness and in weathering resistances such as so-called light resistance and discoloration in darkness and undergo yellowing with the lapse of time. Furthermore, photographic materials which comprise, as a support, a resin-coated paper containing in the resin layer a fluorescent brightening agent of bis(benzoxazolyl)thiophene structure having a substituent, a representative of which is Uvitex OB are deteriorated in whiteness and rather are considerably yellowed as compared with conventional photographic materials when treated with an acidic hardening fixer.